The complement system plays a central role in the clearance of immune complexes and in immune responses to infectious agents, foreign antigens, virus-infected cells and tumor cells. However, inappropriate or excessive activation of the complement system can lead to harmful, and even potentially life-threatening, consequences due to severe inflammation and resulting tissue destruction. These consequences are clinically manifested in various disorders including septic shock, myocardial as well as intestinal ischemia/reperfusion injury, graft rejection, organ failure, nephritis, pathological inflammation and autoimmune diseases. Sepsis, for example, is a major cause of mortality resulting in over 200,000 deaths per year in the United States alone. Despite the major advances in the past several years in the treatment of serious infections, the incidence and mortality from sepsis continues to rise. Therefore, inhibition of excessive or uncontrolled activation of the complement cascade could provide clinical benefit to patients with such diseases and conditions.
The complement system is composed of a group of proteins that are normally present in the serum in an inactive state. Activation of the complement system encompasses mainly two distinct pathways, designated the classical and the alternative pathways (V. M. Holers, In Clinical Immunology: Principles and Practice, ed. R. R. Rich, Mosby Press; 1996, 363-391). The classical pathway is a calcium/magnesium-dependent cascade, which is normally activated by the formation of antigen-antibody complexes. It can also be activated in an antibody-independent manner by the binding of C-reactive protein, complexed with ligand, and by many pathogens including gram-negative bacteria. The alternative pathway is a magnesium-dependent cascade which is activated by deposition and activation of C3 on certain susceptible surfaces (e.g. cell wall polysaccharides of yeast and bacteria, and certain biopolymer materials).
Recent studies have shown that complement can also be activated through the lectin pathway, which involves the initial binding of mannose-binding lectin and the subsequent activation of C2 and C4, which are common to the classical pathway (Matsushita, M. et al., J. Exp. Med. 176: 1497-1502 (1992); Suankratay, C. et al., J. Immunol. 160: 3006-3013 (1998)). Accumulating evidence indicates that the alternative pathway participates in the amplification of the activity of both the classical pathway and the lectin pathway (Suankratay, C., ibid; Farries, T. C. et al., Mol. Immunol. 27: 1155-1161 (1990)). Activation of the complement pathway generates biologically active fragments of complement proteins, e.g. C3a, C4a and C5a anaphylatoxins and C5b-9 membrane attack complexes (MAC), which mediate inflammatory responses through involvement of leukocyte chemotaxis, activation of macrophages, neutrophils, platelets, mast cells and endothelial cells, increased vascular permeability, cytolysis, and tissue injury.
Complement C5a is one of the most potent proinflammatory mediators of the complement system. C5a is the activated form of C5. Complement C5 (190 kD, molecular weight) is present in human serum at approximately 80 μg/ml (Kohler, P. F. et al., J. Immunol. 99: 1211-1216 (1967)). It is composed of two polypeptide chains, α and β, with approximate molecular weights of 115 kD and 75 kD, respectively (Tack, B. F. et al., Biochemistry 18: 1490-1497 (1979)). Biosynthesized as a single-chain pro-molecule, C5 is enzymatically cleaved into a two-chain structure during processing and secretion. After cleavage, the two chains are held together by at least one disulphide bond as well as noncovalent interactions (Ooi, Y. M. et al., J. Immunol. 124: 2494-2498 (1980)).
Primary amino acid structures of human and murine C5 were obtained from cDNA sequencing data (Wetsel, R. A. et al., Biochemistry 27: 1474-1482 (1988); Haviland, D. L. et al., J. Immunol. 146: 362-368 (1991); Wetsel, R. A. et al, Biochemistry 26: 737-743 (1987)). The deduced amino acid sequence of precursor human pre-pro-C5 has 1676 amino acids. The α- and β-chains of mature C5 have 999 and 655 amino acids, respectively. C5 is glycosylated in the C5 α-chain, in particular the asparagine at residue 64.
C5 is cleaved into the C5a and C5b fragments during activation of the complement pathways. The convertase enzymes responsible for C5 activation are multi-subunit complexes of C4b, C2a, and C3b for the classical pathway and of (C3b)2, Bb, and P for the alternative pathway (Goldlust, M. B. et al., J. Immunol. 113: 998-1007 (1974); Schreiber, R. D. et al, Proc. Natl. Acad. Sci. 75: 3948-3952 (1978)). C5 is activated by cleavage at position 74-75 (Arg-Leu) in the α-chain. After activation, the 11.2 kD, 74 amino acid peptide C5a from the amino-terminus portion of the α-chain is released. This C5a peptide shares similar anaphylatoxin properties with those exhibited by C3a, but is 100 times more potent, on a molar basis, in eliciting inflammatory responses. Both C5a and C3a are potent stimulators of neutrophils and monocytes (Schindler, R. et al., Blood 76: 1631-1638 (1990); Haeffner-Cavaillon, N. et al., J. Immunol. 138: 794-700 (1987); Cavaillon, J. M. et al., Eur. J. Immunol. 20: 253-257 (1990)). Furthermore, C3a receptor was recently shown to be important for protection against endotoxin-induced shock in a mouse model (Kildsgaard, J. et al., J. Immunol. 165: 5406-5409 (2000)).
In addition to its anaphylatoxic properties, C5a induces chemotactic migration of neutrophils (Ward, P. A. et al., J. Immunol. 102: 93-99 (1969)), eosinophils (Kay, A. B. et al., Immunol. 24: 969-976 (1973)), basophils (Lett-Brown, M. A. et al., J. Immunol. 117: 246-252 1976)), and monocytes (Snyderman, R. et al., Proc. Soc. Exp. Biol. Med. 138: 387-390 1971)). The activity of C5a is regulated by the plasma enzyme carboxypeptidase N (E.C. 3.4.12.7) that removes the carboxy-terminal arginine from C5a forming the C5a des Arg derivative (Goetzl, E. J. et al., J. Clin. Invest. 53: 591-599 (1974)). On a molar basis, human C5a des Arg exhibits only 1% of the anaphylactic activity (Gerard, C. et al., Proc. Natl. Acad. Sci. 78: 1833-1837 (1981)) and polymorphonuclear chemotactic activity as unmodified C5a (Chenoweth, D. E. et al., Mol. Immunol. 17: 151-161 (1980)). Both C5a and C5b-9 activate endothelial cells to express adhesion molecules essential for sequestration of activated leukocytes, which mediate tissue inflammation and injury (Foreman, K. E. et al., J. Clin. Invest. 94: 1147-1155 (1994); Foreman, K. E. et al., Inflammation 20: 1-9 (1996); Rollins, S. A. et al., Transplantation 69: 1959-1967 (2000)). C5a also mediates inflammatory reactions by causing smooth muscle contraction, increasing vascular permeability, inducing basophil and mast cell degranulation and inducing release of lysosomal proteases and oxidative free radicals (Gerard, C. et al., Ann. Rev. Immunol. 12: 775-808 (1994)). Furthermore, C5a modulates the hepatic acute-phase gene expression and augments the overall immune response by increasing the production of TNFα, IL-1β, IL-6, and IL-8 (Lambris, J. D. et al., In: The Human Complement System in Health and Disease, Volanakis, J. E. ed., Marcel Dekker, New York, pp. 83-118).
The human C5a receptor (C5aR) has been cloned (Gerard, N. P. et al., Nature 349: 614-617 (1991); Boulay, F. et al., Biochemistry 30: 2993-2999 (1991)). It belongs to a superfamily of seven-transmembrane-domain, G protein-coupled receptors. C5aR is expressed on neutrophils, monocytes, basophils, eosinophils, hepatocytes, lung smooth muscle and endothelial cells, and renal glomerular tissues (Van-Epps, D. E. et al., J. Immunol. 132: 2862-2867 (1984); Haviland, D. L. et al., J. Immunol. 154:1861-1869 (1995); Wetsel, R. A., Immunol. Lett. 44: 183-187 (1995); Buchner, R. R. et al., J. Immunol. 155: 308-315 (1995); Chenoweth, D. E. et al., Proc. Natl. Acad. Sci. 75: 3943-3947 (1978); Zwirner, J. et al., Mol. Immunol. 36:877-884 (1999)). The ligand-binding site of C5aR is complex and consists of at least two physically separable binding domains. One binds the C5a amino terminus (amino acids 1-20) and disulfide-linked core (amino acids 21-61), while the second binds the C5a carboxy-terminal end (amino acids 62-74) (Wetsel, R. A., Curr. Opin. Immunol. 7: 48-53 (1995)).
C5a plays important roles in inflammation and tissue injury. In cardiopulmonary bypass and hemodialysis, C5a is formed as a result of activation of the alternative complement pathway when human blood makes contact with the artificial surface of the heart-lung machine or kidney dialysis machine (Howard, R. J. et al., Arch. Surg. 123: 1496-1501 (1988); Kirklin, J. K. et al., J. Cardiovasc. Surg. 86: 845-857 (1983); Craddock, P. R. et al., N. Engl. J. Med. 296: 769-774 (1977)). C5a causes increased capillary permeability and edema, bronchoconstriction, pulmonary vasoconstriction, leukocyte and platelet activation and infiltration to tissues, in particular the lung (Czermak, B. J. et al., J. Leukoc. Biol. 64: 40-48 (1998)). Administration of an anti-C5a monoclonal antibody was shown to reduce cardiopulmonary bypass and cardioplegia-induced coronary endothelial dysfunction (Tofukuji, M. et al., J. Thorac. Cardiovasc. Surg. 116: 1060-1068 (1998)).
C5a is also involved in acute respiratory distress syndrome (ARDS) and multiple organ failure (MOF) (Hack, C. E. et al., Am. J. Med. 1989: 86: 20-26; Hammerschmidt D E et al. Lancet 1980; 1: 947-949; Heideman M. et al. J. Trauma 1984; 4: 1038-1043). C5a augments monocyte production of two important pro-inflammatory cytokines, TNFα and IL-1. C5a has also been shown to play an important role in the development of tissue injury, and particularly pulmonary injury, in animal models of septic shock. (Smedegard G et al. Am. J. Pathol. 1989; 135: 489-497). In sepsis models using rats, pigs and non-human primates, anti-C5a antibodies administered to the animals before treatment with endotoxin or E. coli resulted in decreased tissue injury, as well as decreased production of IL-6 (Smedegard, G. et al., Am. J. Pathol. 135: 489-497 (1989); Hopken, U. et al., Eur. J. Immunol. 26:1103-1109 (1996); Stevens, J. H. et al., J. Clin. Invest. 77: 1812-1816 (1986)). More importantly, blockade of C5a with anti-C5a polyclonal antibodies has been shown to significantly improve survival rates in a caecal ligation/puncture model of sepsis in rats (Czermak, B. J. et al., Nat. Med. 5: 788-792 (1999)). This model shares many aspects of the clinical manifestation of sepsis in humans. (Parker, S. J. et al., Br. J. Surg. 88: 22-30 (2001)). In the same sepsis model, anti-C5a antibodies were shown to inhibit apoptosis of thymocytes (Guo, R. F. et al., J. Clin. Invest 106: 1271-1280 2000)) and prevent MOF (Huber-Lang, M. et al., J. Immunol. 166: 1193-1199 (2001)). Anti-C5a antibodies were also protective in a cobra venom factor model of lung injury in rats, and in immune complex-induced lung injury (Mulligan, M. S. et al. J. Clin. Invest. 98: 503-512 (1996)). The importance of C5a in immune complex-mediated lung injury was later confirmed in mice (Bozic, C. R. et al., Science 26: 1103-1109 (1996)).
C5a is found to be a major mediator in myocardial ischemia-reperfusion injury. Complement depletion reduced myocardial infarct size in mice (Weisman, H. F. et al., Science 249: 146-151 (1990)), and treatment with anti-C5a antibodies reduced injury in a rat model of hindlimb ischemia-reperfusion (Bless, N. M. et al., Am. J. Physiol. 276: L57-L63 (1999)). Reperfusion injury during myocardial infarction was also markedly reduced in pigs that were retreated with a monoclonal anti-C5a IgG (Amsterdam, E. A. et al., Am. J. Physiol. 268:H448-H457 (1995)). A recombinant human C5aR antagonist reduces infarct size in a porcine model of surgical revascularization (Riley, R. D. et al., J. Thorac. Cardiovasc. Surg. 120: 350-358 (2000)).
Complement levels are elevated in patients with rheumatoid arthritis and systemic lupus erythematosus. C5a levels correlate with the severity of the disease state (Jose, P. J. et al., Ann. Rheum. Dis. 49: 747-752 (1989); Porcel, J. M. et al., Clin. Immunol. Immunopathol. 74: 283-288 (1995)). Therefore, inhibition of C5a and/or C5a receptor (C5aR) could be useful in treating these chronic diseases.
C5aR expression is upregulated on reactive astrocytes, microglia, and endothelial cells in an inflamed human central nervous system (Gasque, P. et al., Am. J. Pathol. 150: 31-41 (1997)). C5a might be involved in neurodegenerative diseases, such as Alzheimer disease (Mukherjee, P. et al., J. Neuroimmunol. 105: 124-130 (2000)). Activation of neuronal C5aR may induce apoptosis (Farkas I et al. J. Physiol. 1998; 507: 679-687). Therefore, inhibition of C5a and/or C5aR could also be useful in treating neurodegenerative diseases.
Psoriasis is now known to be a T cell-mediated disease (Gottlieb, E. L. et al., Nat. Med. 1: 442-447 (1995)). However, neutrophils and mast cells may also be involved in the pathogenesis of the disease (Terui, T. et al., Exp. Dermatol. 9: 1-10; 2000); Werfel, T. et al., Arch. Dermatol. Res. 289: 83-86 (1997)). High levels of C5a des Arg are found in psoriatic scales, indicating that complement activation is involved. T cells and neutrophils are chemo-attracted by C5a (Nataf, S. et al., J. Immunol. 162: 4018-4023 (1999); Tsuji, R. F. et al., J. Immunol. 165: 1588-1598 (2000); Cavaillon, J. M. et al., Eur. J. Immunol. 20: 253-257 (1990)). Therefore C5a could be an important therapeutic target for treatment of psoriasis.
Immunoglobulin G-containing immune complexes (IC) contribute to the pathophysiology in a number of autoimmune diseases, such as systemic lupus erthyematosus, rheumatoid arthritis, Goodpasture's syndrome, and hypersensitivity pneumonitis (Madaio, M. P., Semin. Nephrol. 19: 48-56 (1999); Korganow, A. S. et al., Immunity 10: 451-459 (1999); Bolten, W. K., Kidney Int. 50:1754-1760 (1996); Ando, M. et al., Curr. Opin. Pulm. Med. 3: 391-399 (1997)). The classical animal model for the inflammatory response in these IC diseases is the Arthus reaction, which features the infiltration of polymorphonuclear cells, hemorrhage, and plasma exudation (Arthus, M., C.R. Soc. Biol. 55: 817-824 (1903)). Recent studies show that C5aR deficient mice are protected from tissue injury induced by IC (Kohl, J. et al., Mol. Immunol. 36: 893-903 (1999); Baumann, U. et al., J. Immunol. 164: 1065-1070 (2000)). The results are consistent with the observation that a small peptidic anti-C5aR antagonist inhibits the inflammatory response caused by IC deposition (Strachan, A. J. et al., J. Immunol. 164: 6560-6565 (2000)). Together with its receptor, C5a plays an important role in the pathogenesis of IC diseases. Inhibitors of C5a and C5aR could be useful to treat these diseases.
WO01/15731A1 discusses compositions and methods of treatment of sepsis using antibodies to C5a. These antibodies react only with the N-terminal region of the C5a peptide and do not cross-react with C5.
WO86/05692 discusses the treatment of adult respiratory distress syndrome (ARDS) with an antibody specific for C5a or the des Arg derivative thereof. It also discloses the treatment of sepsis by administering this antibody. This antibody was produced in response to the C5a des Arg derivative because it is more immunogenic, but will elicit antibodies cross reactive with C5a. U.S. Pat. No. 5,853,722 discusses anti-C5 antibodies that block the activation of C5 and thus, the formation of C5a and C5b.
U.S. Pat. No. 6,074,642 discusses the use of anti-C5 antibodies to treat glomerulonephritis. These antibodies also block the generation of C5a and C5b, inhibiting the effect of both C5a and the formation of C5b-9. U.S. Pat. No. 5,562,904 discusses anti-C5 antibodies that completely block the formation of MAC.
In other discussions of anti-C5 antibodies, the antibodies disclosed block activation of C5 and its cleavage to form C5a and C5b (Vakeva, A. P. et al., Circulation 97:2259-2267 (1998); Thomas, T. C. et al., Mol. Immunol. 33:1389-1401 (1996); Wang, Y. et al., Proc Natl Acad Sci. 93:8563-8568 (1996); Kroshus, T. et al., Transplantation 60:1194-1202 (1995); Frei, Y. et al., Mol. Cell. Probes 1:141-149 (1987)).
Monoclonal antibodies cross-reactive with C5, C5a, or C5a des Arg have been reported (Schulze, M. et al., Complement 3: 25-39 (1986); Takeda, J. et al., J. Immunol. Meth. 101: 265-270 (1987); Inoue, K., Complement Inflamm. 6: 219-222 (1989). It has also been reported that monoclonal antibodies cross-reactive with C5 and C5a inhibited C5a-mediated ATP release from guinea pig platelets (Klos, A. et al., J. Immunol. Meth. 111: 241-252 (1988); Oppermann, M. et al., Complement Inflamm. 8: 13-24 (1991)).